Entity DeclarationsPort Clause (cont.)
The port mode of the interface describes the direction in which data travels with respect to the component
The five available port modes are:
- In - data comes in this port and can only be read
- Out - data travels out this port
- Buffer - data may travel in either direction, but only one signal driver may be on at any one time
- Inout - data may travel in either direction with any number of active drivers allowed; requires a Bus Resolution Function
- Linkage - direction of data flow is unknown
The mode indicates the direction of the flow of data across that port. This flow of data is defined with respect to the component.
The five port modes available:
1. IN -- indicates that the (only) signal driver is outside this component
2. OUT -- indicates that the (only) signal driver is within this component. Note that until 1076-1993, a component could not read its own OUT ports.
3. BUFFER -- indicates that there may signal drivers inside and outside this component. However, only one of these drivers can be driving the signal at any one time.
4. INOUT -- indicates that there may be signal drivers inside and outside this component. Any number of these drivers can be driving the signal simultaneously, but a Bus Resolution Function is then required to determine what values the signal will assume.
5. LINKAGE -- indicates that the location of the signal drivers is not known. This mode type only indicates that a connection exists.